Field of the Invention
The present invention relates to concrete including a plurality of fiber rings, and more particularly, the present invention relates to concrete in which a plurality of fiber rings are included to prevent the concrete from being fractured due to cracks developed therein.
Generally, a composite material is made by mixing two or more materials, to maximally utilize advantages of the respective materials and to compensate for disadvantages of the respective materials. Among various composite materials, a fiber-reinforced composite material is prepared by a unidirectional mixing of long-fibers, mixing of woven-fibers, mixing of short-fibers or mixing of long-fibers and short-fibers, depending upon a reinforcing method by fibers. As materials for a substrate and a fiber of a fiber-reinforced composite material, polymer, metal, ceramic, concrete, etc. are mainly used.
Concrete, which is widely used in the fields of civil-engineering or architecture, has a certain brittleness so that it is apt to be fractured by tensile load or dynamic load. Further, concrete has a disadvantage in that it is difficult to suppress the formation and growth of cracks developed therein. In order to resolve these drawbacks of concrete, that is, to improve its mechanical property by increasing tensile strength and suppressing the formation and growth of local cracks, a plurality of linear fibers having a straight configuration are included in concrete in an irregularly distributed manner. This is called fiber-reinforced concrete or fiber concrete.
Referring to FIGS. 1A through 1C, three different configurations of linear fibers according to the prior arts are illustrated. A linear fiber 20a, which has a straight configuration with both ends bent, is shown in FIG. 1A. Another linear fiber 20b, which is partially curved on several spaced-apart points thereby to be deformed, is shown in FIG. 1B. Still another linear fiber 20c, for increasing adhesion force through bearing pressure by concrete, is shown in FIG. 1C. On the other hand, referring to FIG. 2, there is shown a cross-sectional view illustrating a state in which a plurality of linear fibers having various configurations, as shown in FIGS. 1A through 1C, are disorderly distributed in concrete.
As can be readily seen from the above descriptions, most fibers currently used as a reinforcing material for concrete have a basically straight configuration which may be partially changed in its cross-section.
However, the linear fibers of the prior arts, constructed as mentioned above, suffer from defects as described below. First, since the linear fiber has tensile strength which is much larger than pull-out strength, when cracks are formed and grown in the concrete, the linear fiber is likely to be pulled out rather than be fractured. According to this, because the linear fiber does not generate tensile force anymore, it cannot properly perform its original function of reinforcing tensile strength of the concrete. Second, especially in the case where concrete is used in building a road, since both ends of the linear fiber may be exposed to the outside, sharp ends of the linear fiber can hurt the human body and scratch an object, thereby breaking it. Third, because the linear fibers are apt to be entangled and poorly distributed, workability of the concrete is reduced and reinforcing effect by the linear fibers is deteriorated.
Particularly, in the case of a linear fiber, when cracks are formed in concrete, an angle between a lengthwise direction of the linear fiber and a cracking direction of the concrete varies, and according to this, pull-out strength of the linear fiber is changed. Referring to FIGS. 3A through 3C, there are shown cross-sectional views for explaining the phenomenon that pull-out strength of a linear fiber is changed as an angle between a lengthwise direction of the linear fiber and a cracking direction of concrete varies. First, FIG. 3A illustrates a situation in which a cracking direction C of concrete 10 or a cracking surface S of the concrete 10 is perpendicular to a lengthwise direction of a linear fiber 20, that is, .theta..sub.1 =90.degree.. At this time, fracturing force Fs equals pull-out load P, and when the fracturing force Fs of the concrete 10 is larger than the pull-out load P of the linear fiber 20, the linear fiber 20 is pulled out from the concrete 10. Next, FIG. 3B illustrates another situation in which concrete 10 is cracked while defining an angle .theta..sub.2 with respect to a lengthwise direction of a linear fiber 20. At this time, an equation, Fs=P.multidot.sin .theta..sub.2, is established by relations between fracturing force Fs and pull-out load P in equilibrium of force. Consequently, since an inequality, 0&lt;sin .theta..sub.2 &lt;1, is given while the pull-out load P of the linear fiber 20 is constant, the linear fiber 20 is pulled out by the fracturing force which is smaller than that in FIG. 3A where .theta..sub.1 =90.degree.. Also, while shearing force P.multidot.cos .theta..sub.2, which is another component force of the pull-out load P, is offset by other linear fibers, it reduces the strength of the linear fiber 20. On the other hand, FIG. 3C illustrates still another situation in which a cracking surface S of concrete 10 is parallel to a lengthwise direction of a linear fiber 20, that is, .theta..sub.3 =0. At this time, since pull-out load P of the linear fiber 20 is 0, the linear fiber 20 cannot perform its original function of reinforcing tensile strength of concrete 10, at all. Actually, it is extremely rare for cracks of the concrete 10 to be generated in the direction which is perpendicular to the lengthwise direction of the linear fiber 20, and in most cases, the cracking surface S of the concrete 10 defines the angle .theta..sub.2 with respect to the lengthwise direction of the linear fiber 20. In this circumstance, because the pull-out load of the linear fiber 20, which is applied to the concrete 10, is smaller by sin .theta..sub.2 than that in the case that .theta..sub.1 =90.degree., the linear fiber 20 included in the concrete 10 is pulled out by a smaller fracturing force. As a result, the linear fiber of the prior arts cannot sufficiently perform its original function of reinforcing tensile strength of concrete.